1. Field of the Invention
The present invention relates to a sheet feeding device feeding sheets of paper such as cut sheets of paper that is applicable to image forming apparatuses represented by copiers and printers. Moreover, the present invention relates to a document feeding apparatus and an image forming apparatus equipped with such a paper feeding apparatus. Hereinafter, a document that contains image data to be printed and sheets of paper to which that image data is to be printed will be collectively referred to as “sheets”.
2. Description of Related Art
In image forming apparatuses represented by copiers and printers, a paper feeding apparatus is indispensable for feeding cut sheets of paper and the like. In many paper feeding apparatuses used in image forming apparatuses, a plenty of sheets of a document or paper are stacked in advance inside containers thereof such as a document loading tray or a paper feeding cassette, and then the uppermost one of the stacked sheets inside the containers is separated and fed, one after another, therefrom. Such a paper feeding apparatus is employed in a document feeding apparatus, cassette-type feeding section, manual paper feed section, and the like incorporated in an image forming apparatus.
For paper feeding apparatuses feeding sheets of a document or paper out of the containers, there are two types of mechanisms adoptable, namely a roller feeding type and a sheet suction feeding type, and generally the former is widely used. According to the roller feeding type mechanism, a pickup roller comes into contact with the uppermost one of stacked sheets of a document or paper, and hands it onto paper feeding rollers on the downstream side in a paper feeding direction, so that the paper feeding rollers convey the stacked sheets, one after another, out of the containers.
During the paper feeding, a pickup roller of the paper feeding apparatus and the uppermost of a bundle of documents or paper need to make contact with each other; on the other hand, when the paper feeding is not performed, since the containers may often be loaded or supplied with sheets of a document or paper, at least either the pickup roller or the stacked sheets needs to be moved back so that they do not make contact with each other. To this end, some of the paper feeding apparatuses are provided with a mechanism that is movable between a paper feeding position at which the pickup roller and the uppermost one of the stacked sheets of a document or paper are in contact with each other and a moved-back position at which one of them is away from the other.
Among such paper feeding apparatuses as described above, one example of a paper feeding apparatus pressing a downstream-side portion, in a conveyance direction, of document sheets stacked inside the document loading tray, toward a pickup roller can be seen in JP-H6-255806. The automatic document feeding apparatus (paper feeding apparatus) disclosed in this patent publication is provided with a movable guide plate (lift plate) permitting the downstream-side portions, in the conveyance direction, of stacked sheets of a document to move up and down.
In the automatic document feeding apparatus disclosed in the aforementioned patent publication, an eccentric cam plate provided for movable plate operating means is so rotated by use of a motor as to lift up and down the movable guide plate with the result that the downstream-side portion, in the conveyance direction, of the uppermost one of the stacked sheets can be moved to a paper feeding position. In this apparatus, the cam is brought into contact with a movable plate lever fixed to a supporting shaft of the movable guide plate so as to thereby transmit movement of the cam along the shape thereof directly to the movable guide plate; thus, repeated up- and down-movement of the cam imposes a load on the supporting shaft and hence may lead to the problem of deforming the axial line between the movable guide plate and the movable plate lever, and the like. This creates a concern that the relative position between the movable guide plate and the movable plate lever may be changed from the initial state when they were assembled together, and that the height of the movable guide plate may thus be variable. This may adversely affect the paper feeding operation accordingly.
Moreover, since the movable plate lever is fixed to the rotation shaft of the movable guide plate, these members are in a close positional relationship. Thus, it is necessary to arrange driving force sources including the cam and a motor rotating that cam in the vicinity of the movable guide plate. This inconveniently constitutes a restriction on the construction of the driving force sources. Specifically, in a case where the driving force sources are apart from the movable guide plate, additional mechanism components such as a belt and a plurality of gears are required. This creates another concern that the greatly increased number of materials and components used leads to an increase in costs. In addition, given that a space for arranging those belt and gears should be ensured, there is a possibility to increase the size of the apparatus.